Measure the wheel width from bead seat to bead seat
Find the wheel centerline by dividing the width in half
Measure the backspacing from the wheel mounting surface to the inner lip
Convert backspacing to offset by subtracting half the wheel width
Use the formula: Offset = Backspacing – Half of wheel width
Convert the result to millimeters if needed
Positive offset means the mounting surface is toward the outside face
Negative offset means the mounting surface is toward the inside face
Zero offset means the mounting surface is centered on the wheel
Verify the measurement with a wheel offset calculator if available